Harry Ward Leonard (February 8, 1861 – February 18, 1915) was an American electrical engineer and inventor. He is best known for his invention, the Ward Leonard motor control system. Equipment based on this invention remained in service into the 21st century.

Early life and heritage

Harry Ward Leonard was born on February 8, 1861, in

Cincinnati, Ohio Cincinnati ( ) is a city in the U.S. state of Ohio and the county seat of Hamilton County. Settled in 1788, the city is located at the northern side of the confluence of the Licking and Ohio rivers, the latter of which marks the state line wi ...

, to Ezra George Leonard and Henrietta Dana Ward. He was the fourth of their six children. He was a great great grandson of

American Revolutionary War The American Revolutionary War (April 19, 1775 – September 3, 1783), also known as the Revolutionary War or American War of Independence, was a major war of the American Revolution. Widely considered as the war that secured the independence of t ...

General

Artemas Ward Artemas Ward (November 26, 1727 – October 28, 1800) was an American major general in the American Revolutionary War and a Congressman from Massachusetts. He was considered an effective political leader, President John Adams describing him as ...

. In 1895, he was married to Carolyn Good in Geneva, Switzerland. As a student at the

Massachusetts Institute of Technology The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the ...

(MIT), Leonard was instrumental in founding the student newspaper, '' The Tech'', and served as the president of the paper’s board of directors. He graduated from MIT in 1883.

Career

After graduating from MIT, Leonard was employed by

Thomas Edison Thomas Alva Edison (February 11, 1847October 18, 1931) was an American inventor and businessman. He developed many devices in fields such as electric power generation, mass communication, sound recording, and motion pictures. These inventi ...

to help introduce the Edison central-station electric power distribution system. Within four years, he was promoted to the position of general superintendent of the Western Electric Light Company of

Chicago, Illinois (''City in a Garden''); I Will , image_map = , map_caption = Interactive Map of Chicago , coordinates = , coordinates_footnotes = , subdivision_type = Country , subdivision_name ...

. The following year, he established Leonard and Izard, a firm that set up

electric railways A railway electrification system supplies electric power to railway trains and trams without an on-board prime mover or local fuel supply. Electric railways use either electric locomotives (hauling passengers or freight in separate cars), e ...

and generating stations. In 1889, his firm was acquired by Edison and Leonard became the general manager of the Edison operations in the United States and Canada. In 1896, Leonard organized and became president of Ward Leonard Electric as an Edison company in

Hoboken, New Jersey Hoboken ( ; Unami: ') is a city in Hudson County in the U.S. state of New Jersey. As of the 2020 U.S. census, the city's population was 60,417. The Census Bureau's Population Estimates Program calculated that the city's population was 58,690 i ...

. In 1898, he left the Edison organization and incorporated his ow
Ward Leonard Electric Company
on February 19, 1898, in the village of Bronxville in Westchester County, New York. While working for Edison, Leonard patented a number of inventions and he continued developing new ideas throughout his career. He was granted patents for more than 100 inventions of electrical distribution and control systems and related equipment.

The Ward Leonard motor control system

The Ward Leonard motor control system was Mr. Leonard’s best known and most lasting invention. It was introduced in about 1891 and soon became the most widely used type of

electric motor An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a wire winding to generate for ...

speed control Cruise control (also known as speed control, cruise command, autocruise, or tempomat) is a system that automatically controls the speed of a motor vehicle. The system is a servomechanism that takes over the throttle of the car to maintain a ste ...

. In a Ward Leonard system, a

prime mover Prime mover may refer to: Philosophy *Unmoved mover, a concept in Aristotle's writings Engineering * Prime mover (engine), motor, a machine that converts various other forms of energy (chemical, electrical, fluid pressure/flow, etc) into energy ...

drives a

direct current Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or eve ...

(DC) generator at a constant speed. The armature of the DC generator is connected directly to the armature of a DC motor. The DC motor drives the load equipment at an adjustable speed. The motor speed is adjusted by adjusting the output

voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to ...

of the generator using a

rheostat A potentiometer is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider. If only two terminals are used, one end and the wiper, it acts as a variable resistor or rheostat. The measuring instrume ...

to adjust the excitation

current Currents, Current or The Current may refer to: Science and technology * Current (fluid), the flow of a liquid or a gas ** Air current, a flow of air ** Ocean current, a current in the ocean *** Rip current, a kind of water current ** Current (stre ...

in the

field Field may refer to: Expanses of open ground * Field (agriculture), an area of land used for agricultural purposes * Airfield, an aerodrome that lacks the infrastructure of an airport * Battlefield * Lawn, an area of mowed grass * Meadow, a grass ...

winding. The motor field current is usually not adjusted, but the motor field is sometimes reduced to increase the speed above the base speed. The prime mover is usually an

alternating current Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in whic ...

(AC) motor, but a DC motor or an

engine An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power ...

might be used instead. To provide the DC field excitation power supply, Ward Leonard systems usually include an exciter generator that is driven by the prime mover. Although only technical specialists are likely to be familiar with Ward Leonard systems, many millions of people have ridden in

elevator An elevator or lift is a cable-assisted, hydraulic cylinder-assisted, or roller-track assisted machine that vertically transports people or freight between floors, levels, or decks of a building, vessel, or other structure. They a ...

s powered by Ward Leonard drives. From the 1920s through the 1980s most electrically driven elevators used Ward Leonard control and many systems remained in use at the beginning of the 21st century. Many variations of the Ward Leonard system have been implemented, but they have generally continued to be called Ward Leonard systems. H. Ward Leonard and many others have patented auxiliary

control systems A control system manages, commands, directs, or regulates the behavior of other devices or systems using control loops. It can range from a single home heating controller using a thermostat controlling a domestic boiler to large industrial c ...

used to regulate the motor speed as required to automatically perform specific tasks such as controlling pump speed to regulate flow. Mechanical types of

adjustable-speed drive Motor drive means a system that includes a motor. An adjustable speed motor drive means a system that includes a motor that has multiple operating speeds. A variable speed motor drive is a system that includes a motor and is continuously variabl ...

s and other electrical types continued to be used and new types developed after the Ward Leonard system was introduced. Electron tube types of DC motor controls began to be developed in the 1920s but electronic controls didn’t seriously begin to displace the Ward Leonard system until

thyristor A thyristor () is a solid-state semiconductor device with four layers of alternating P- and N-type materials used for high-power applications. It acts exclusively as a bistable switch (or a latch), conducting when the gate receives a current ...

controlled drives were developed in the late 1960s. By the mid-1970s, Ward Leonard drives were rapidly becoming obsolete, but the replacement of existing Ward Leonard drives has continued past the end of the 20th century.

Sudden death

H. Ward Leonard was an active member of the

American Institute of Electrical Engineers The American Institute of Electrical Engineers (AIEE) was a United States-based organization of electrical engineers that existed from 1884 through 1962. On January 1, 1963, it merged with the Institute of Radio Engineers (IRE) to form the Insti ...

, publishing technical papers, attending meetings and making presentations. He died suddenly on February 18, 1915, in New York while attending the annual dinner of the American Institute of Electrical Engineers.

References

Citations

General references

* * * {{DEFAULTSORT:Leonard, Harry Ward 1861 births 1915 deaths American electrical engineers American inventors Massachusetts Institute of Technology alumni People from Cincinnati Engineers from Ohio